1. Field of the Invention
The present invention relates to a bearing manufacturing method.
2. Description of the Related Art
A spindle motor arranged to rotate a disk is typically installed in a disk drive apparatus, such as, for example, a hard disk drive. Qualities such as, for example, low vibration, high rotational accuracy, and high durability are demanded of the spindle motor. A fluid dynamic bearing is sometimes used as a bearing of the spindle motor to provide these qualities.
The fluid dynamic bearing includes a stationary bearing member, a rotatable bearing member, and a lubricating oil arranged therebetween. While the fluid dynamic bearing is operating, a dynamic pressure is induced in the lubricating oil by a dynamic pressure groove defined in the stationary bearing member or the rotatable bearing member. As a result, the rotatable bearing member accurately and smoothly rotates with respect to the stationary bearing member. In the case of the fluid dynamic bearing as described above, if gas is introduced into the lubricating oil inside the bearing, the gas may, for example, become a gas bubble to reduce performance of the fluid dynamic bearing. Therefore, in a process of manufacturing the fluid dynamic bearing, it is necessary to deaerate the lubricating oil and prevent gas from being introduced into the lubricating oil after the lubricating oil is deaerated. A known method of manufacturing a fluid dynamic bearing is described in, for example, JP-A 2002-213452.
In a general process of injecting the lubricating oil into the fluid dynamic bearing, a pressure inside an oil tank, from which the lubricating oil is supplied, is made higher than a pressure inside a chamber in which the bearing is arranged, and the lubricating oil is supplied from the oil tank to the chamber using the pressure difference. This method involves increasing the pressure inside the oil tank, from which the lubricating oil is supplied, and this may cause gas to be dissolved into the lubricating oil which has once been deaerated.
In the manufacturing method described in JP-A 2002-213452, a pressure inside a first vacuum chamber in which the bearing is arranged is set at a value equivalent to or slightly lower than a set value of a pressure inside a second vacuum chamber in which a lubricating fluid is stored. Thus, when an on-off valve is opened, the lubricating fluid inside the second vacuum chamber flows toward the first vacuum chamber because of gravity. However, the method described in JP-A 2002-213452 has a problem in that it is difficult to precisely control the amount of the lubricating fluid to be supplied, because gravity is used for supply of the lubricating oil.